Description of Related Art
The size of recording or reproducing apparatus of the above type, such as a video tape recorder (VTR), has been substantially reduced during recent years. The rotary drum unit of the apparatus has accordingly become smaller and the recording tape has come to be wrapped around the rotary drum within a smaller space, which has resulted in a complex shape for the traveling path of the tape.
FIG. 1 of the accompanying drawings shows by way of example the tape path of a compact 8 mm VTR, including point A, which is the point at which the tape leaves the rotary drum. FIG. 2 is an enlarged view of a part of the rotary drum unit of the VTR of FIG. 1, illustrating point A thereof and its environment.
Referring to FIG. 1, the rotary drum unit 12 has magnetic heads arranged on the periphery thereof at a given spacing distance and includes a rotary upper drum and a stationary lower drum. A capstan 13 with associated pinch roller 14 move the tape 7 at a given speed. The apparatus includes supply reel 15 and take-up reel 16.
The tape path shown in FIG. 1 is defined by guide posts 17 to 25. The guide posts 20 and 21 are disposed on a supply side and the guide posts 22 and 23 on a take-up side adjacent point A. The tape 7 is wrapped at a given angle around the drum unit 12 by the guide posts. A tension regulator pin 17 is provided for detecting the tension of the tape. The guide posts 18, 19, 24 and 25 further define the tape path beyond that defined by guide posts 20 to 23.
The tape transport characteristic of the described arrangement is now discussed. In normal recording or reproduction, the tape 7 is pulled out from the supply reel 15 at a given degree of tension. After this, the tape 7 is wrapped around the drum unit 12 while being supported by the guide posts. The capstan 13 and the pinch roller 14 then jointly act to move the tape 7 to allow it to be wound on the take-up reel 16. Under this condition, the tape tension gradually increases between the supply reel 15 and the capstan 13.
In the case of tape travel in the reverse direction, the tape 7 is pulled out from the take-up reel 16 and is immediately moved by the capstan 13 and the pinch roller 14. After that, the tape 7 is taken up by the supply reel 15 through the drum unit 12 and the guide posts. In this instance, since the tape 7 is wound on the supply reel 15 at a constant torque, the tape tension gradually decreases between the supply reel 15 and the capstan 13.
At the tape parting point A on the drum unit 12 near the capstan 13, the tape tension varies to a great degree with the traveling direction of the tape 7. When the tape 7 normally travels in the recording or reproducing direction, the tape is stretched relative to the guide posts in a plane, as is shown by broken lines in FIG. 2. On the other hand, in the event of reverse tape travel, a decrease in tape tension, in conjunction with the rigidity of the tape itself, causes the tape to travel in a curved state from the guide posts as is shown in FIG. 2 by full lines.
This tendency for tape tension variation is enhanced as drum diameter becomes smaller with such reduction in size of the apparatus, since the tape wrapping angle increases accordingly as the diameter of the rotary drum decreases.
Where the tape curves in its reverse travel, the tape wrapping angle increases relative to the drum unit 12. As a result, at the parting point between the drum unit 12 and the tape 7, the area of the tape 7 contacting with the drum unit 12 increases and this unstable tape travel increases the load imposed on the tape driving system. In a worst case, tape 7 begins to loosen and this presents a serious problem.